Field
The present invention relates to a light emitting diode and, more particularly, to a light emitting diode that includes a transparent conductive layer facilitating current spreading, and a method for manufacturing the same.
Discussion of the Background
Recent developments of various display devices have increasingly attracted attention to transparent materials suited for light transmission characteristics. A display device converts electric signals into light and thus employs a plurality of electrodes in order to transfer the electric signals. Since opaque electrodes block light and thus reduce visibility, it is necessary to provide transparent electrodes that can secure both transparency and electrical conductivity.
Such a transparent electrode can exhibit transparency in the visible wavelength range when having an energy band gap of 2.5 eV or more. That is, since light in the wavelength range of blue light to UV light has shorter wavelengths and higher energy, a transparent electrode having a smaller energy band gap cannot transmit light from blue light to UV light which are in the wavelength range of higher energy. Accordingly, in order to transmit light from blue light to UV light in the wavelength range of higher energy, a material having a larger energy band gap is employed as the transparent electrodes. Among such conductive materials exhibiting transparency, ITO has a larger energy band gap.
ITO is an acronym of indium tin oxide. Since ITO exhibits high electrical conductivity, has a band gap of about 4.3 eV and a larger work function, exhibits good light transmittance in the visible wavelength, and allows an easy patterning process, ITO is easy to use in manufacture of displays or light emitting diodes.
Thereamong, a light emitting diode can be formed with a plurality of semiconductor layers including a light emitting layer, wherein one of the semiconductor layers adjoins an electrode through which light emitting signals are input. Here, since the semiconductor layer has higher specific resistance than the electrode, there is difficulty in ohmic contact therebetween.
Thus, a transparent electrode layer for ohmic contact may be further formed between the semiconductor layer and the electrode. In other words, the transparent electrode layer may be interposed therebetween in order to reduce contact resistance between the semiconductor layer and the electrode.
Moreover, since the transparent electrode layer is required to transmit light emitted from the light emitting layer, it is necessary for the transparent electrode layer to exhibit transparency. ITO exhibiting transparency and electrical conductivity is generally used as a material for the transparent electrode layer.
However, when the transparent electrode layer is thickly formed using ITO, a large thickness of ITO can cause increase in light loss due to rapid decrease in light transmittance and increase in light absorption rate thereof.
On the other hand, when the transparent electrode layer is thinly formed using ITO in order to prevent light absorption, contact resistance becomes unstable due to unstable ohmic contact between the transparent electrode layer and the semiconductor layer, thereby causing increase in operation voltage due to local current crowding and increase in forward voltage.
Moreover, ITO has problems such as high material costs due to use of indium (In) as a main raw material and operation instability caused by high reducing properties of indium (In) and tin (Sn) in hydrogen plasma by diffusion of indium (In).